Oil and gas production has been developing rapidly over the last decade with the use of new technologies and materials. One advance has been the development of dissolvable materials for use during fracturing and other downhole procedures. The dissolvable ball when used with a sliding sleeve or ball seat allow fracturing, signaling, and pressure modulated processes to be conducted, then the ball dissolves allowing hydrocarbons to travel through the production well. Dissolvable materials require a known dissolution rate at bottom hole conditions including temperature, pressure, and solution.
Well completion occurs after the well has been drilled to depth. Completion, is the process of making a well ready for production. The bottom of the well is prepared according to required specifications including well bore casings, production casing, down hole tools, cementing, perforating, and stimulation as required. Once all equipment is delivered and the well cemented, the completion string integrity is tested prior to stimulation and/or production.
The most common completion practice is to cement the production casing and use shaped charge perforating guns to establish communication between the reservoir and the wellbore. A standard completion is depicted in FIG. 1 and contains a variety of commonly used tools in the ‘shoe’ of the well. Although different assemblies may be used dependent upon the well, casing diameter, production diameter, well bore, pressure, reservoir type and other factors, a typical well completion comprises running a production casing with shoe assembly through the surface casing/hole to the bottom of the well. Some common features include the cementing head 102, top pug, 110, bottom plug 112, float collar 114, centralizer 116, guide shoe 118. These are used with drilling fluid 108, displacement fluid 104, and cement slurry 106. A guide shoe 118 ensures the shoe assembly reaches depth without catching in the casing, well bore, and guides the shoe to the bottom of the hole past ledges and sidewall collapse, as the production casing passes through deviated sections of the well bore.
Centralizers 116 may be placed at intervals along the production casing to keep the production casing in the center of the well bore, ensure even distribution of the cement 120, and protect the production casing from wear on the side of the well bore and casing. A majority of wells completed today are horizontal wells and multiple centralizers are required to ensure the production casing does not rest on the bottom of the long, horizontal well bore.
A float collar serves many purposes during completion and can act as a final landing point for various types of equipment used during the completion process. The float collar provides a ‘landing point’ for the wiper plugs as well as any other equipment required at the shoe of the well. Equipment may include mechanical valves, backpressure valves, and the like. In some embodiments a separate shoe guide, centralizer, and float collar may be used. In other embodiments, a single piece my function as a guide shoe, centralizer and/or float collar to conserve space and minimize the length of shoe assembly.
Once the shoe assembly is in place, the well is cemented to protect and seal the wellbore. The cementing process involves careful calculation of the production casing and production casing annulus volumes, return volume, and amount of cement required to seal the annulus of the well. Typically after drilling, a wiper or bottom plug is placed in front of the cement slurry. The bottom plug has a diaphragm that bursts once the plug is seated on the float collar. The bottom plug may have a catch, that interlocks with the float collar to prevent movement of the wiper plug when it is seated. The bottom plug fills the inside diameter of the production casing and is typically made of a flexible material, such as rubber, plastic or other pliable material. The bottom plug may also have a metal or solid elastomeric body with flexible fins that ‘wipe’ the sides of the production casing. The bottom plug pushes any debris to the bottom of the well and reduces the amount of material stuck inside the production casing. The bottom plug is hollow and once the diaphragm bursts, the cement flows through the bottom plug, float collar, centralizers, and guide shoe into the annulus of the well bore.
A top plug 110 is run after the slug of cement. The top plug ensures the cement is pushed intact through the production casing, through the bottom plug, and into the annulus of the well. The top plug is typically solid and must resist large changes in pressure to ensure that the cement is pushed completely through the production casing, through the bottom plug, and through the check or backpressure valve. Once the top plug lands on the bottom plug, there is a dramatic increase in surface pressure signaling the end of the cementing procedure. The increase in pressure verifies the integrity of the production casing and confirms there is no leak-off of pressure. Because the top plug is a solid plug it completely blocks flow through shoe assembly. The cement sets in the shoe assembly and the well must be perforated to obtain fluid communication with the well bore. FIG. 1B shows a shoe assembly filled with cement after the cementing process. Lavaure, et al., (U.S. Pat. No. 5,890,537) describes a casing or liner cementing method including the steps of positioning lower and upper wiper plugs having elastomer cups.
Degradable materials have been used to create downhole tools previously. Fripp & Walton, (WO2016032619A1 & WO2016025682A1) describe downhole tools having at least one component made of a doped magnesium alloy solid solution that at least partially degrades in the presence of an electrolyte. Hoffman, et al., (US20140116721A1) describes closed toe required for pressure testing tubing installed in a well.
A wet shoe as described by Williamson & Stratton (U.S. Pat. No. 9,279,295) occurs when cement does not set around or obstruct the float valve or check valves at the end of the liner. If during cementing the float or check valves are obstructed, the guide shoe and toe of the well must be drilled out to obtain a wet shoe. A wet shoe enables subsequent operations after cementing including pumping plugs, perforating guns and other equipment to the toe of the well.
After the final production casing string for a well (Oil, Gas, and/or Water) is cemented, the production casing well becomes a closed loop system. In order to establish communication to the formation, perforations or hydraulic actuated toe-valves have to be deployed in order to establish a connection. What is required is a new shoe equipment cementing process that provides a tight cement seal for the production casing and shoe assembly but allows fluid communication with the backside of the well bore upon completion.